The present invention relates to a system for sensing the flow rate and temperature of air moving through a conduit such as a heating and/or cooling duct and, more particularly, to such a system wherein signals representing flow rate and temperature are generated from a single sampling or sensing head.
A building's environmental control system most often includes a chiller and heating plant for supplying chilled and hot water to heat exchange coils located in the ducts of the various fan systems which distribute controlled air throughout the building. A fan system might include a fan which draws air from a mixing chamber which mixes outdoor air and return air and discharges that air through heating and cooling coils and humidifiers to the spaces supplied by the fan system.
Depending upon the sophistication of the control system for the air being supplied to the spaces of the building, various parameters will be controlled. For example, all systems will typically control the temperature of the space by controlling both the temperature and the amount of air being supplied to the space. In addition, humidity, static pressure, and air quality can all be controlled. Moreover, local codes often require a minimum amount of fresh air to be supplied to the spaces within a building. In such systems, therefore, it is necessary to sense both the temperature and the volume of the air being discharged to the spaces within a building. The sensing of the amount of air being supplied through a fan system is often determined by a flow station while the temperature of the air passing through a fan system is often determined by a separate temperature sensor.